In paragraph 5, the vines covered the wooden frame "like a green curtain." What does this phrase mean?

On Saturday mornings, Danny's grandfather, whom he called Ông, rode the bus to a community garden on the east side of Houston. This spring, Danny's mother said that Danny had to go with him.

Danny did not see the point. The grocery store down the street sold vegetables in neat plastic bags, and nobody there had to kneel in the dirt to get them.

Ông's garden plot was small, only about as long as a car. He handed Danny a trowel and showed him how to dig a hole as deep as his finger. Into each hole went two pale seeds. "Bitter melon," Ông said. "Your grandmother's favorite."

For two weeks, nothing happened. Danny checked every Saturday and found only dirt. "Maybe the seeds were bad," he said. Ông just poured water along the rows and said, "Seeds do not listen to complaining."

In the third week, small green leaves pushed up through the soil. By June, the vines had climbed the wooden frame Ông had built and covered it like a green curtain. Bumpy, pale green melons hung underneath.

Ông picked the first melon and turned it over in his hand. Then he told Danny a story Danny had never heard: how, as a boy in Vietnam, he had helped his own grandmother grow the same vegetable behind her house, and how she had cooked it with eggs for him whenever he was sick.

That evening, Danny's mother cooked the melon with eggs. It was so bitter that Danny made a face at the first bite. Ông laughed. Danny took a second bite anyway, and then a third.

The next Saturday, Danny was waiting at the bus stop before his grandfather got there.